1. Field of the Invention
The present invention relates to an electromechanical transducer such as an ultrasonic transducer, and to a method of manufacturing the electromechanical transducer. More specifically, the present invention relates to a technology of improving the reliability of an electromechanical transducer.
2. Description of the Related Art
Ultrasonic transducers perform conversion from an electrical signal to an ultrasonic wave and conversion from an ultrasonic wave to an electrical signal, and are used, among others, as probes for medical imaging or non-destructive inspection. One form of ultrasonic transducer is a capacitive micromachined ultrasound transducer (CMUT). A CMUT generally includes a substrate, which has a lower electrode, a membrane, which is supported to the substrate by a supporting portion formed on the substrate, and an upper electrode. The CMUT uses a voltage applied between the lower electrode and the upper electrode to cause the membrane to vibrate and emit ultrasonic waves. The CMUT also receives ultrasonic waves which cause the membrane to vibrate and, from the resultant change in the capacitance between the lower electrode and the upper electrode, detects the ultrasonic waves.
Conventionally, CMUTs have been manufactured with the use of surface micromachining, bulk micromachining, or the like. The conventional CMUT manufacture may employ a wiring method in which at least one combination of a membrane and a cavity (namely, at least one cell) on a silicon substrate constitutes a single element, and the element is connected to a circuit board, with the silicon substrate itself acting as a lower electrode and as electrical through-wafer interconnects. In a known example of this wiring method, elements of a CMUT are two-dimensionally arranged into arrays by providing a groove that separates the lower electrode of one element from the lower electrode of another element to electrically isolate the elements from one another, and then leading their respective wirings out from the back (see U.S. Patent No. 2006/0075818 A1 and U.S. Patent No. 2007/0013269 A1). In another known method, a high level of insulation between adjacent elements is obtained by filling the groove with an insulating substance such as epoxy resin.
However, with a conventional CMUT that has a groove for separating one lower electrode from another as described above, there is a possibility of a conductive foreign object entering the groove during the manufacture process or while the CMUT is in use, and bridging the lower electrodes adjoined to the groove to cause a short circuit.